1. Field of the Invention
The present invention relates in general to a movable barrier operator for opening and closing a movable barrier or door. More particularly, the invention relates to a movable barrier operator with a designed response to the movable barrier encountering an obstruction.
2. Discussion of the Related Art
A number of garage door operators have been sold over the years. Most garage door operators include a head unit containing a motor having a transmission connected to it, which may be a chain drive or a screw drive, which is coupled to a garage door for opening and closing the garage door. The garage door is typically positioned for movement along a pair of door rails that are mounted to a ceiling of the garage. For reasons of safety garage door operators, when in a closing mode and contacting an obstruction reverse and open the door in order to prevent damage to property and injury to persons.
Known garage door operators typically include optical detection systems located near the bottom of the travel of the door to prevent the door from closing on objects or on persons that may be in the path of the door. In addition to optically sensing obstructions, garage door operators are known to include systems that detect an operating speed of the garage door operator, and when an obstruction interferes with movement of the garage door, and hence, slows the operating speed of the garage door opener, the direction of the garage door movement is reversed.
Occasionally, known garage door operators reverse directions in response to being slowed by false obstructions that impede the path of the garage door. Such false obstructions, for example, dirt in the garage door rails, causes the speed of the garage door to slow down just enough to trigger the garage door operator to reverse directions. These false obstructions are an annoyance to the users of barrier movement systems.